Electrical power transformers and transmission cables generally contain a dielectric insulating oil to prevent shorting of the electrical potential within the device. It is important that these oils contain very little free or dissolved water. Generally, dielectric oils must contain no more than about ten parts per million water.
Transformers are periodically serviced by heating the dielectric oil above about 200.degree. F. under a high vacuum to remove built-up dissolved water. This is generally accomplished by circulating the oil through a heating and evacuation system mounted on a mobile service truck. This process is quite expensive, requiring special expertise to operate the equipment and additional manpower to set up and then disconnect the mobile system.
Moreover, new transformer and cable dielectric oils generally contain more than 10 ppm water, and must be dried before being injected into such electrical equipment. Heating/evacuating systems typically are used to dry these new dielectric oils as well.
U.S. Pat. No. 4,019,977 to Hachadoorian et al. discloses a demister-coalescer for removing water from oil. The oil containing dissolved water is passed through a vessel containing a dispersing material. The vessel is maintained under a vacuum, and water vapor is removed from the oil.
U.S. Pat. No. 3,398,208 to Ward discloses the use of a molecular sieve bed for drying a stream of hydrocarbon-containing water. The wet hydrocarbon is passed through the bed where the water is absorbed into the pores of the molecular sieve. When the molecular sieve bed becomes saturated with water, and retained water is detected in the effluent hydrocarbon stream, the bed is then taken out of service and regenerated in a conventional manner to remove the absorbed water.
It would be desirable to develop apparatus for drying dielectric oils in a manner that does not require the downtime and expense of the conventional heating/evacuating systems, and which can consistently and reliably reduce the dissolved water content of the oils to a value below about 10 ppm.